VACCINATION WITH A LOW-ONCOGENIC STRAIN OF ROUS-SARCOMA VIRUS PREVENTS VISCERAL TUMORS IN CHICKENS

The oncogenic potential of different strains of Rous sarcoma virus (RS V) varies significantly in two Mhc(B) congenic chicken lines CB and CC and in their F-1 hybrids with the unrelated inbred line IA. The Bryan high-titer pseudotype of RSV of antigenic subgroups D and B (BH-D, an d BH-B) was highly oncogenic, eliciting mostly fatal, progressively gr owing tumors. Visceral tumor formation and erythroblastosis were seen after challenge with BH-B in CB and CC chickens, but not in their F-1 hybrids with IA. Tumor regression induced by a low-oncogenic RSV strai n PR-C elicited a protective immunity capable of preventing not only t he progressive growth of challenge tumors at the site of inoculation, but also visceral tumor formation and erythroblastosis.